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Metal Detection and X-Rays - Likes and Dislikes


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christian.stadler

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Posted 17 April 2019 - 07:36 AM

Hello,

 

I am new to the forum and interested in people's perception of Metal Detection and X-Ray equipment.

 

What is your experience regarding these machines, what are you missing in today's solutions?

What would really be beneficial to support you in your Food Safety tasks?

 

Regards,

Christian

 



tamdongnai

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Posted 17 April 2019 - 07:58 AM

Dear Christian

Metal detection: you only find metal like iron, but not for stainless steel

X ray: detect stranger object in finished product (physical risks)

At Milk powder factory: Metal detection install before filling machine and X ray will install after completed filling.



Charles.C

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Posted 17 April 2019 - 10:39 AM

Dear Christian

Metal detection: you only find metal like iron, but not for stainless steel

X ray: detect stranger object in finished product (physical risks)

At Milk powder factory: Metal detection install before filling machine and X ray will install after completed filling.

 

Hi tamdongnai,

 

^^^ Actually stainless steel (eg 316) can typically be detected although at a lower sensitivity than ferrous/non-ferrous.

 

@ Christian - it would be nice if MD sensitivity was 10x better for all food matrices/orientations while simultaneously giving few false positives.


Kind Regards,

 

Charles.C


LDG_Honey

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Posted 17 April 2019 - 12:13 PM

^^^ Actually stainless steel (eg 316) can typically be detected although at a lower sensitivity than ferrous/non-ferrous.

 

That entirely depend on the mode of your detector : ~±90° for conductive ''dry'' products and ~±0° for resistive ''wet'' product.

non-ferrous and ferrous metals are closer to the ±90° angle and Stainless steel is closer to the 0° angle.
In our case, we are in ''wet'' mode and Stainless steel is 10 times more sensitive than for Non-ferrous or ferrous metals.


Edited by LDG_Honey, 17 April 2019 - 12:14 PM.


Charles.C

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Posted 17 April 2019 - 12:47 PM

That entirely depend on the mode of your detector : ~±90° for conductive ''dry'' products and ~±0° for resistive ''wet'' product.

non-ferrous and ferrous metals are closer to the ±90° angle and Stainless steel is closer to the 0° angle.
In our case, we are in ''wet'' mode and Stainless steel is 10 times more sensitive than for Non-ferrous or ferrous metals.

 

Hi LDG,

 

I believe you but unfortunately I have no idea what the angles are talking about.

My experience is with a conventional conveyor belt / MD system for retail/intermediate frozen foods

 

IIRC, every MD sensitivity spec. I have seen quoted so far on this forum has diameter SS sphere > Fe/non-Fe (axial line)

 

can you provide a link to the characteristics you describe ?


Kind Regards,

 

Charles.C


Charles.C

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Posted 17 April 2019 - 02:02 PM

Hi LDG,

 

I am guessing you may (somehow) be referring to detection of wire contaminants / orientation effects ?


Kind Regards,

 

Charles.C


christian.stadler

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Posted 17 April 2019 - 02:21 PM

Hello again,

 

well obviously sensitivity - especially on stainless steel - is a decisive criteria and that is also the one topic where metal detector providers are constantly seeking for improvements.

I was also curious about other likes or dislikes / pains and gains which would be beneficial.

 

Let me pull one example:

Major industries which have high requirements regarding security and safety (e.g. Aviation, Power Plants) has specific requirements regarding usability of user interfaces.

There are international norms regarding usability which have to be followed to prevent false settings of security equipment.

In terms of food safety, the guidelines in that direction could be described "low level".



LDG_Honey

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Posted 17 April 2019 - 02:46 PM

I'm drafting information from my background in chemistry (university level) and a thorough read through my MD user manual. Excuse me in advance if i'm saying dubious hypothesis or if i am plainly wrong. Feel free to correct me.

 

The metal detector (at least mine) is made of 2 coils. The input coil and the detector coil. The central coil, also called the oscillator, generates a magnetic field which induce a current into the input coil. But the input coil is built on both sides of the oscillator, meaning that when one side tries to push electrons one way, the other side pushes them the other way, leaving a net signal (current) of 0.

 

When a piece of metal passes through the coil (or anything in fact), the magnetic field is changed, creating an imbalance between both sides of the input coil and generating a signal. 

The nature of the metal (or any material) dictate how the magnetic field is deformed. On one side we got diamagnetic materials and the other we have paramagnetic material. Within the paramagnetic domain, we have some freaky behavior called Superparamagentism, ferromagnetism and ferrimagnetism. They all do the same thing as paramagnetism, just way stronger and, for some, longer.

 

When a paramangetic material is subjected to a magnetic field, it allows it to pass through while weakly strengtening it, the net effect is that it is attracted. It the reverse for diamagnetic materials, the generate a field of similar strenght but opposite direction, the net effect is that it is repulsed by the magnetic field.

 

Ferrous materials are either Ferrimagnetic or ferromagnetic, non ferrous are usually paramagnetic. Don't mind about superparamagnetism, it mostly happens with nanoparticles and i'd be surprised if you worked with those in the food industry.

 

Copper, silver, gold, aluminium, zinc, cadmium metals, for example, are diamagnetic, just like Carbon, Silicium, Nitrogen and the like

 

Now since the central coil that generate the magnetic field is connected to an oscillator, the field changes direction and goes back (a revolution) every determined interval of time (a frequency), usually this value is in Hertz (Hz) or per seconds. It follow a classic Sinusoidal wave.

Paramagnetic materials amplify the wave, increasing it height. Diamagnetic material, dampen or even cancel it. Both give a signal to the input coil, it is just different depending on where we are in time, compared to the oscillator wave, or the phase.

 

We can program the detector to look only of a portion of the sinusoidal wave, like the peaks of the wave that is at ±90°, or slightly around. Usually at 0°, there is no magnetic field. The angle of this portion is the phase.

 

But what does Stainless steel do in all this? it is clearly paramagnetic and should amplify the wave. Yes, it does...

But the phenomenon is not instantaneous. Good conductors like copper, aluminium or even iron react quickly to changes in the magnetic field. Stainless steel does not, it take close to half a revolution to react to changes.

This means that around 0°, there is a magnetic field that can be detected. This is why it is easier to detect Stainless steel at lower frequencies. This is also why, when testing the MD, we use stainless steel beads that are much bigger, more bulk means stronger magnetic field.

 

When we are looking for a phase around 0°, the signal is processed in a way that we negate the oscillator wave. Other metals can still be detected, since they are not exactly synchronised, but the dephased signal from SS is extremely clear.

 

Now you don't usually program your MD around what kind of metal you want to find, but around your product. You do not want to see the effect of your product in your detector.

Wet product tends to be good conductors and will interact with the magnetic field like most metals do. Low frequencies and a phase around 0° helps to ignore it.

Dry product are usually bad conductors and interact with the magnetic field like SS does. High frequencies and a phase around ±90° can cancel any effect it would have to the magnetic field.

 

Now i believe I've explained it all. I might go back and edit later if i find I lost myself in my explanations.



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Charles.C

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Posted 17 April 2019 - 02:48 PM

Hi christian,

 

I anticipate most FS Operatives regard metal/X-ray detectors as tools.

I doubt there is much of an anthropomorphic relationship.

 

Technicians may have a different viewpoint of course.

 

@ LDG - Can have a look through this text which probably covers the basics -

 

Attached File  Metal_Detection Guide.pdf   3.17MB   29 downloads

 

PS - our posts overlapped. Thks yr detailed comments. I have a feeling that the theory has changed somewhat in my attachment.


Edited by Charles.C, 17 April 2019 - 03:06 PM.
added

Kind Regards,

 

Charles.C


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The Food Scientist

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Posted 17 April 2019 - 04:12 PM

Hi there, 

 

It depends on your food safety system, processes and many other things. For example. I work at a spice company. Our process has little to no risk of metal contamination. rather it has the risk of other foreign material like plastics and twigs and such. So we will incorporate x-rays in our process. 


Everything in food is science. The only subjective part is when you eat it. - Alton Brown.


Charles.C

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Posted 18 April 2019 - 11:37 AM

Hello,

 

I am new to the forum and interested in people's perception of Metal Detection and X-Ray equipment.

 

What is your experience regarding these machines, what are you missing in today's solutions?

What would really be beneficial to support you in your Food Safety tasks?

 

Regards,

Christian

 

Hi Christian,

 

Apologies that yr specific OP got a bit side-tracked. It happens sometimes.

 

Perhaps you could expand yr "experience" query in respect to what "kind" of experiences you are mainly interested in ? eg IMEX of MDs -

 

Sensitivity?                     8

Accuracy ?                     8

Effectiveness ?               9     

Applicability/Scope?        8

Reliability?                      8

Accidents ?                    10

Cost?                              7

Maintenance?                 9

 

One fact afaik is that for a lot of Processes the MD is (rightly or wrongly) the "qualifier" for a haccp plan (ie  to possess a minimum of 1 CCP [Yes, I know this is a debatable comment]). What you might call a "Critical" Experience. :smile:


Kind Regards,

 

Charles.C


christian.stadler

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Posted 23 April 2019 - 08:35 AM

Hi Christian,

 

Apologies that yr specific OP got a bit side-tracked. It happens sometimes.

 

Perhaps you could expand yr "experience" query in respect to what "kind" of experiences you are mainly interested in ? eg IMEX of MDs -

 

Sensitivity?                     8

Accuracy ?                     8

Effectiveness ?               9     

Applicability/Scope?        8

Reliability?                      8

Accidents ?                    10

Cost?                              7

Maintenance?                 9

 

One fact afaik is that for a lot of Processes the MD is (rightly or wrongly) the "qualifier" for a haccp plan (ie  to possess a minimum of 1 CCP [Yes, I know this is a debatable comment]). What you might call a "Critical" Experience. :smile:

 

Thank you Charles,

don't worry - I know that discussions in forums can get side-tracked.

 

Totally agree on your "debatable comment", but you hit the nail on spot. For a lot of Processes, an MD is a qualifier for a HACCP plan. But then if a processor has to have at least one MD, it should be one that makes the life of a Food Safety Professional easier and my question was going in that direction. What would make the life easier besides just making detection performance better and more cost-efficient.



Scampi

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Posted 23 April 2019 - 04:53 PM

IMHO MD do not work in all applications or conditions..........density seems to be a real sticking point, but that may just be set up

 

Cost is also an issue and an xray machine is significantly more money (and sometimes much physically larger)  

 

Depending on where you are, there may be additional H&S rules, as x ray exposure could be an issue (but one would think this isn't really a problem)


Please stop referring to me as Sir/sirs


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christian.stadler

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Posted 24 April 2019 - 02:06 PM

IMHO MD do not work in all applications or conditions..........density seems to be a real sticking point, but that may just be set up

 

Cost is also an issue and an xray machine is significantly more money (and sometimes much physically larger)  

 

Depending on where you are, there may be additional H&S rules, as x ray exposure could be an issue (but one would think this isn't really a problem)

 

Thanks Scampi!

Yes, as with many sensors there are restrictions. In this case, as MD's are working with an electromagnetic field, there are restrictions regarding the surrounding conditions which can influence the metal detector. For example the belt conveyor design, other machinery etc. can have influence on the electromagnetic field.

Product density itself is far less of influence than the so called "Product Effect" which is basically the conductivity of the product due to moisture, salt, temperature variation among others. This product effect tends to limit detectability of certain metals (especially stainless steel) in traditional metal detectors.

However, newer developments are metal detectors which inspect the product with multiple frequencies simultaneously and therefore are able to more or less cancel the product effect and achieve very high detectability while reducing false reject rate at the same time. There are only a handful manufacturers with this technology.

 

With X-Ray you are right, in many countries there are also other rules / legislation coming into consideration as these machines are working with radiation. Whilst a typical machine has less emission to the user than let's say an intercontinental flight (and therefore can be considered as not harmful), regulations are still regulations.






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